Current semiconductor processing typically comprises forming an integrated circuit containing a plurality of conductive patterns on vertically stacked levels connected by vias and insulated by inter-layer dielectrics. As device geometry plunges into the deep sub-micron range, chips comprising five or more levels of metallization are formed.
In manufacturing multi-level semiconductor devices, it is necessary to form each level with a high degree surface planarity, avoiding surface topography, such as bumps or areas of unequal elevation, i.e., surface irregularities. In printing photolithographic patterns having reduced geometry dictated by the increasing demands for miniaturization, a shallow depth of focus is required. The presence of surface irregularities can exceed the depth of focus limitations of conventional photolithographic equipment. Accordingly, it is essential to provide flat planar surfaces in forming levels of a semiconductor device. In order to maintain acceptable yield and device performance, conventional semiconductor methodology involves some type of planarization or leveling technique at suitable points in the manufacturing process.
A conventional planarization technique for eliminating or substantially reducing surface irregularities is CMP wherein abrasive and chemical action is applied to the surface of the wafer undergoing planarization. The polishing pad is employed together with a chemical agent to remove material from the wafer surface.
FIG. 1 is a schematic top plan view of a conventional CMP apparatus 11 comprising a rotatable platen 15 on which is mounted a polishing pad 17 for polishing semiconductor substrate S. The polishing pad 17 can be a conventional slurry-type pad having a plurality of concentric circumferential grooves 19 as illustrated, or a fixed abrasive-type polishing pad.
CMP apparatus 11 further comprises a pivot arm 21, a holder or conditioning head 23 mounted to one end of the pivot arm 21, a pad conditioner 25, such as a pad embedded with diamond crystals, mounted to the underside of the conditioning head 23, a slurry source such as a slurry/rinse arm 27, and a substrate mounting head 29 operatively coupled to platen 15 to urge substrate S against the working surface of polishing pad 17. Pivot arm 21 is operatively coupled to platen 15, and maintains conditioning head 23 against the polishing pad 17 as the pivot arm 21 sweeps back and forth across the radius of polishing pad 17 in an arcing motion. Slurry/rinse arm 27 is stationarily positioned outside the sweep of the pivot arm 21 and the conditioning head 23 coupled thereto.
In operation, the substrate S is placed face down beneath the substrate mounting head 29, and the substrate mounting head 29 presses the substrate S firmly against the polishing pad 17. Slurry is introduced to the polishing pad 17 via slurry/rinse arm 27, and platen 15 rotates as indicated by arrow R1. Pivot arm 21 scans from side to side in an arcing motion as indicated by arrow S1.
When the pad is grooved, then grooves 19 channel the slurry (not shown) between the substrate S and the polishing pad 17. The semi-porous surface of the polishing pad 17 becomes saturated with slurry which, with the downward force of the substrate mounting head 29 and the rotation of the platen 15, abrades and planarizes the surface of the substrate S. The diamond crystals (not shown) embedded in the rotating conditioner 25 continually roughen the surface of the polishing pad 17 to ensure consistent polishing rates. Pad cleaning must be performed frequently to clean polishing residue and compacted slurry from the polishing pad 17.
Conventional pad cleaning techniques employ rinsing wherein the substrate mounting head 29 is removed from contact with the polishing pad 17, the supply of slurry from the slurry/rinse arm 27 is turned off, and a rinsing fluid such as deionized water is supplied via the slurry/rinse arm 27. However, merely rinsing the polishing pad following CMP is often ineffective in removing polishing residues, particularly after CMP of metal films, because polishing by-products stick to the polishing pad.
Conventional polishing pads employed in abrasive slurry processing typically comprise a grooved porous polymeric surface, such as polyurethane, and the abrasive slurry varied in accordance with the particular material undergoing CMP. Basically, the abrasive slurry is impregnated into the pores of the polymeric surface while the grooves convey the abrasive slurry to the wafer undergoing CMP. Another type of polishing pad is a fixed abrasive pad wherein abrasive elements are mounted on a backing. When conducting CMP with a fixed abrasive pad, a chemical agent without abrasive particles is applied to the pad surface.
When conducting CMP on a metal-containing surface, e.g., Cu or a Cu alloy, the working or polishing surface of the polishing pad undergoes changes believed to be caused by, inter alia, polishing by-products resulting from the reaction of metal being removed from the wafer surface, such as Cu, with components of the CMP slurry or chemical agent, e.g., oxidizer, complexing agents and inhibitors. Such by-products typically deposit onto the polishing pad and accumulate causing a colored stain or glazed area. Such a surface exhibits a lower coefficient of friction and, hence, a substantially lower material removal rate by adversely impacting polishing uniformity and increasing polishing time. In addition, such glazing causes scratching of the wafer surface. Conventional approaches to remedy pad glazing include pad conditioning, as with nylon brushes or diamond disks for removing the deposited by-products from the polishing pad surface. However, such a conventional remedial approach to the glazing problem is not particularly effective in completely removing glazing. Pad conditioning with a diamond disk also greatly reduces pad lifetime.
There exists a need for methodology enabling the planarization of a wafer surface containing Cu or Cu alloy with reduced pad glazing. There exists a particular need for methodology enabling CMP of a wafer surface containing Cu or Cu alloys at high production throughput.